(CNN) -- Congolese rebels seized a major military camp and a spacious gorilla park in a renewed bout of heavy fighting that sent thousands fleeing, according to the United Nations and park officials.

Young gorillas play in Congo's Virunga Park, which was taken over Sunday by rebels fighting army forces.

The fighting comes after a tenuous week-old U.N. brokered cease-fire between rebels and government forces fell apart Sunday.

Fighting between the rebels under renegade Gen. Laurent Nkunda and Congolese army regulars in the eastern province of North Kivu of the Democratic Republic of the Congo displaced thousands of civilians, according to U.N. spokesman Michele Bonnardeaux.

The rebels also seized the headquarters of Virunga National Park in eastern Congo after intense fighting with the Congolese army, according to a statement by park officials.

The rebels have used Virunga Park as a base but have never seized its headquarters before.

The 3,000 square mile (7,800 square kilometer) park has a gorilla facility and is home to 200 of the 700 endangered mountain gorillas in existence.

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"Over 50 rangers were forced to flee into the forests and abandon the park station, in fear of their lives," the park statement said.

"They have seized the entire gigantic infrastructure [of the park headquarters] which is stategically very close to the main road heading north into Goma," said park spokeswoman Samantha Newport by phone from Goma, about 40 kilometers from the fighting.

Newport said the rebels have set up roadblocks so the rangers are making their way through woods south to safety.

She said the gorillas and other wildlife in the park are in danger of getting caught in the crossfire.

A park ranger described the takeover.

"When the rebels started approaching the park station we thought we were all going to be killed," said Park Ranger Bareke Sekibibi, 29, who spoke by cell phone from the forest earlier as he fled, according to the park statement.

" We are not military combatants, we are park rangers protecting Virunga's wildlife."

Although the civil war in the Congo officially ended in 2003, recent fighting in eastern Congo between government forces and rebels has caused tens of thousands to flee their homes

The conflict and humanitarian crisis in Congo have taken the lives of some 5.4 million people since 1998, and that 45,000 people continue to die there every month, according to an International Rescue Committee report in January.